Among the machines used as commercial dishwashers are front-loading machines, rack push-through machines and conveyor-type dishwashers, while under-counter dishwashers are generally used in the domestic sector. The loading of front-loading machines with dish racks in which the dishes are held and the removal of the dish racks from front-loading machines takes place from the front. In the case of rack push-through machine, the dish racks, laden with dirty dishes, are manually pushed into the machine from a feeding side and, after completion of the cleaning program, are manually removed from the machine from a delivery side. Conveyor-type dishwashers, which are distinguished in comparison with the previously mentioned types of dishwasher by a high throughput of items to be washed per unit of time, have at least one spray zone, but usually more than one spray zone, through which the items to be cleaned are automatically conveyed.
In each spray zone of a conveyor-type dishwasher, at least one spray operation can be executed. In the case of conveyor-type dishwashers, it is generally customary for the dishes to be cleaned of major soil in a first spray zone (pre-wash zone) by spraying with a dishwashing detergent solution, while thorough cleaning of the dishes takes place in a subsequent spray zone (wash zone) by renewed spraying with a dishwashing detergent solution. Thereafter follows at least one, mostly two spray zones (rinse zones) in which dishes are sprayed with a rinse aid solution, in order to finally rinse the dishes completely clear of dirt particles and clear of dishwashing detergent solution. The final-rinse operation is generally carried out at temperatures of 80° C. to 85° C., before the dishes are then conveyed into a drying zone for drying.
A conveyor-type dishwasher with four spray zones is described in U.S. Pat. No. 3,598,131. The spray zones are designed as a pre-wash zone, as a wash zone, as a rinse zone and as a final-rinse zone, the items to be cleaned being conveyed continuously through these spray zones one after another in suitable dish racks. The individual zones are separated from one another by suspended flexible “curtains”. In the pre-wash zone, a solution at about 49° C. is sprayed onto the items to be cleaned by means of spray nozzles, in order to remove particles of food from the items to be cleaned. Subsequently, in the wash zone, a mixture of water and dishwashing detergent at about 66° C. and in turn, subsequently in the rinse zone, hot water at temperatures of about 77° C. is sprayed onto the items to be cleaned by means of spray nozzles. To achieve disinfection of the items to be cleaned, in the final-rinse operation, hot water at about 82° C. is sprayed onto the items to be cleaned by means of spray nozzles in the final-rinse zone.
A similar conveyor-type dishwasher, likewise with four spray zones, is known from U.S. Pat. No. 3,789,860. U.S. Pat. No. 3,789,860 describes a pre-wash zone, in which larger particles of food are removed, a subsequent main wash zone for accomplishing effective cleaning of the items to be cleaned, a main-rinse zone and, finally, a final-rinse zone. The temperature in the dishwasher is approximately 46° C. in the first zone and increases zone by zone up to a temperature of approximately 82° C. in the final-rinse zone.
The device of U.S. Pat. No. 4,231,806 is suitable for dishwashers with a number of spray zones and describes means for creating a barrier in the form of a fluid curtain, a fluid curtain preferably being created respectively at the entry and exit of a wash zone and at the entry and exit of a final-rinse zone. The fluid curtain at the entry and exit of the wash zone greatly reduces the escape of vapour from the wash zone.
In the medical sector, U.S. Pat. No. 6,632,291 discloses methods for the washing, rinsing and/or antimicrobial treatment of medical instruments, equipment, transporting carts and animal cages. Washing takes place at temperatures between 30° C. and 80° C., preferably between 35° C. and 40° C., while usually-rinse is carried out at temperatures between 40° C. and 80° C. and a final-rinse is carried out at increased temperatures at approximately 80° C. to 95° C. The antimicrobial treatment is performed with an antimicrobial agent. The method described can be carried out automatically in a wash apparatus which has a number of stations.
U.S. Pat. No. 4,788,992 describes an ultrasonic cleaning method and an apparatus for carrying out ultrasonic cleaning of elongated strip material. After the ultrasonic cleaning, the strip material is sent past dewatering blowers and subsequently past spray nozzles of a number of rinse chambers, before it is heated and dried in a final step.
U.S. Pat. No. 6,354,481 relates to the processing of electronic components and in particular to a compact apparatus for remelting and subsequently cleaning electronic components, in particular BGA components. The cleaning zone has a wash zone and a rinse zone, and a hot-air blower may also be arranged downstream of them, whereby temperatures in the wash zone are at 49° C. to 71° C. and in the rinse zone at 49° C. to 99° C.
U.S. Pat. No. 2,235,885 describes an apparatus for washing (cleaning) and disinfecting glassware, the apparatus having a chamber which can be tightly closed for the spray operation. Within the chamber, positioning carriers are provided for holding the glassware to be cleaned. Also arranged in the chamber, underneath the positioning carriers, are tubes with upwardly directed spraying means and, in the upper part of the chamber, there are tubes with downwardly directed openings, which are fed with hot water, cold water or steam through corresponding supply lines. The feeding in of hot water and steam into the pipework is manually set by means of a hot-water valve, and the feeding in of cold water into the pipework is manually set by means of a cold-water valve.
In the case of washing operation described in U.S. Pat. No. 2,235,885, glassware to be cleaned is first rinsed and disinfected with hot water and steam in the chamber. Subsequently, a cold-water valve is progressively opened and, after the cold-water valve has been opened, the hot-water valve is closed, so that then only cold water is introduced into the chamber and the glassware to be cleaned is chilled with cold water in the final-rinse operation.
In U.S. Pat. No. 4,070,204 a washing method is described which can be carried out in a dishwasher which includes a cleaning chamber into which cold water, hot water or a combination of both can be introduced optionally. The washing method begins with at least one cold pre-wash, which is followed by a hot wash. Subsequently, a cold-water rinse and at least one hot-water final-rinse are carried out.
The development of dishwashers and dishwashing methods, in particular in the commercial sector, is dominated today by the objective of energy and water conservation, which is becoming increasingly important for environmental reasons. Nevertheless, in particular in the case of commercial dishwashers, the throughput, which is the amount of items cleaned per unit of time, and the washing quality should not be deteriorated. The working conditions of the operator of a dishwasher are also considerably impaired in the region of the dishwasher by vapours which escape, with the result that an improvement in this area is also desirable.
Furthermore, apart from thorough cleaning, disinfection of the items to be cleaned should also be carried out. In the field of dishwasher technology, disinfection means killing micro-organisms at a level that is neither harmful to health nor impairs the quality of food. In the case of some wash methods, disinfection is achieved by the use of chemical disinfection components, but this has disadvantages from aspects concerning the environment and safety at work. Disinfection by adequately intense heating of the items to be cleaned is also known.
It would be desirable to provide an improved operating method and an improved conveyor-type dishwasher of the type as indicated which—while maintaining high cleaning quality—have in particular low energy and water consumption, are sufficiently productive and can be used without reservations from aspects concerning the environment and safety at work.